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Changes in resource availability can alter plant growth, the influence of plants on soil characteristics, and, ultimately, plant–soil feedback (PSF). Previous studies often show that invasive plants can outperform native plants under high but not low resource conditions. However, it remains unclear whether under low resource conditions, invaders can outperform natives in the long term by generating more positive or less negative PSFs. Using three non-native invasive and three non-invasive native annual Asteraceae plants, we conducted a two-phase pot experiment, where in the first, conditioning generation plants were grown to induce changes in soil characteristics, and in the second, bioassay generation plants were regrown to evaluate how they respond to these soils. Half of the pots received a nutrient addition treatment in the conditioning generation. We found significant species-specific effects of conditioning on most of the soil characteristics, and some soil characteristics were significantly correlated with bioassay generation biomass of a subset of species, but neither species nor invasive or native status affected bioassay generation biomass. All invasive species generated neutral PSFs across soil nutrient conditions. The native Emilia sonchifolia tended to condition the soil that favored its own growth more than others, and under low nutrient conditions, the native Eclipta prostrata conditioned the soil that disfavored its own growth more than others. These results indicate that invaders may not outperform natives through PSFs under low resource conditions, and increasing resource availability may change the types of PSFs for some native but not invasive plants. [ABSTRACT FROM AUTHOR]

Hybridization between introduced and related native species has been suggested to be a key driving force of evolutionary processes in invasions that may be accelerated by increasing nitrogen (N) deposition. We carried out two experiments to compare the competitive ability of a newly-reported putative hybrid ( Sphagneticola calendulacea × Sphagneticola trilobata) to that of its invasive paternal parent and investigate its response to different N additions. Growth of the hybrid increased by 39.62 ± 15.69 % when grown with the native parent but showed no significant changes when grown with the invasive parent. Growth of invasive S. trilobata showed no significant changes when grown with the other two taxa. The hybrid and invasive parent inhibited the growth of the native parent by 33.27 ± 15.26 % and 78.56 ± 3.13 %, respectively. Low level N addition (50 kg N ha) enhanced the growth of both the hybrid and native parent, whereas medium and high levels of N additions (150, 300 kg N ha) had no effects on hybrid growth but decreased native parent growth. However, all N treatments had no significant effects on the growth of the invasive parent. Our results suggest that the hybrid is an equal competitor to its invasive parent and is more susceptible to N deposition. Therefore, this hybrid could be a threat to native diversity but may decline more than the invasive parent under high N conditions. [ABSTRACT FROM AUTHOR]

Mono-dominance by invasive species provides opportunities to explore determinants of plant distributions and abundance; however, linking mechanistic results from small scale experiments to patterns in nature is difficult. We used experimentally derived competitive effects of an invader in North America, Acroptilon repens, on species with which it co-occurs in its native range of Uzbekistan and on species with which it occurs in its non-native ranges in North America, in individual-based models. We found that competitive effects yielded relative abundances of Acroptilon and other species in models that were qualitatively similar to those observed in the field in the two ranges. In its non-native range, Acroptilon can occur in nearly pure monocultures at local scales, whereas such nearly pure stands of Acroptilon appear to be much less common in its native range. Experimentally derived competitive effects of Acroptilon on other species predicted Acroptilon to be 4–9 times more proportionally abundant than natives in the North American models, but proportionally equal to or less than the abundance of natives in the Eurasian models. Our results suggest a novel way to integrate complex combinations of interactions simultaneously, and that biogeographical differences in the competitive effects of an invader correspond well with biogeographical differences in abundance and impact. [ABSTRACT FROM AUTHOR]

• Invasive plants effect on soil C accumulation and soil microbes' role are unclear. • Photoassimilated-13C' distribution and utilization by microbes were determined. • Invasive plants photoassimilated more C and transferred the C faster to soils. • Soil C accumulate rate was modulated by soil microbes. Exotic plant invasion alters the structure and coverage of terrestrial vegetation and affects the carbon (C) stocks in ecosystems. Previous studies have shown the increases in the C stocks with increasing invasive plants, but these results remain contentious. Soil microbial communities are usually altered by plant invasion, which potentially influences the C cycling underground. We hypothesized that the plant invasion-caused dynamic changes in soil microbes would lead to the corresponding change in soil C accumulation. Using greenhouse experiments we simulated different invader intensities through varying the relative abundance of invasive species Mikania micrantha and its co-occurring native species Paederia scandens. By analyzing 13C-phospholipid fatty acid we found the invasive M. micrantha assimilated more 13C and transferred faster the fixed 13C through different tissues to soils, as compared to native P. scandens. Soil microbial components, i.e., i15:0, 16:0, 10Me16:0, 18:1w9c and 18:2w6,9 were mainly using the photo-assimilated 13C. In addition, we found a hump-shaped relationship between soil net 13C accumulate rate and rhizosphere microbial biomass, indicating that the soil C accumulation may be either enhanced or reduced in invaded ecosystems, depending on microbe abundance. [ABSTRACT FROM AUTHOR]

The soil fungal community plays an important role in forest ecosystems and is crucially influenced by forest secondary succession. However, the driving factors of fungal community and function during temperate forest succession and their potential impact on succession processes remain poorly understood. In this study, we investigated the dynamics of the soil fungal community in three temperate forest secondary successional stages (shrublands, coniferous forests, and deciduous broad‐leaved forests) using high‐throughput DNA sequencing coupled with functional prediction via the FUNGuild database. We found that fungal community richness, α‐diversity, and evenness decreased significantly during the succession process. Soil available phosphorus and nitrate nitrogen decreased significantly after initial succession occurred, and redundancy analysis showed that both were significant predictors of soil fungal community structure. Among functional groups, fungal saprotrophs and pathotrophs represented by plant pathogens were significantly enriched in the early‐successional stage, while fungal symbiotrophs represented by ectomycorrhiza were significantly increased in the late‐successional stage. The abundance of both saprotroph and pathotroph fungal guilds was positively correlated with soil nitrate nitrogen and available phosphorus content. Ectomycorrhizal fungi were negatively correlated with nitrate nitrogen and available phosphorus content and positively correlated with ammonium nitrogen content. These results indicate that the dynamics of fungal community and function reflected the changes in nitrogen and phosphorus availability caused by the secondary succession in temperate forests. The fungal plant pathogen accumulated in the early‐successional stage and ectomycorrhizal fungi accumulated in the late‐successional stage may have a potential role in promoting forest succession. These findings contribute to a better understanding of the response of soil fungal communities to secondary forest succession and highlight the importance of fungal communities during the successional process. [ABSTRACT FROM AUTHOR]

Leaf stoichiometry and its biogeography play vital roles in nutrient cycling of plant communities. To understand the potential drivers of leaf stoichiometry in karst ecosystems, we measured leaf morphological traits (dry mass content (DM), specific leaf area (SLA)), and biochemical traits (C, N, P, K and Ca stoichiometry) of 53 species of different functional groups, as well as soil properties, across seven karst sites in Southwest China, and explored the relationships between these leaf traits and environmental factors. The results showed that: (1) in karst areas of Southwest China, there were higher leaf C and Ca concentrations as well as higher N/P and K/P ratios compared to other ecosystems, plants were more limited by P rather than by N; (2) mean annual temperature positively influenced leaf N, P, and Ca, while mean annual precipitation exerted more influence on leaf K; (3) a strong phylogeny signal was detected in leaf N (p < 0.05), and significant influence of species composition on the variance of leaf N, K, and Ca was observed (p < 0.05); (4) the influence of soil properties on leaf P and Ca, and the influence of leaf features (SLA and DM) on leaf K were also observed based on a variance partitioning analysis. Abiotic factors such as soil, site, and climate were more important than biotic factors (leaf features and phylogeny) in determining leaf N, P, and Ca. In general, the driving factors exhibited a synergistic effect on leaf stoichiometry across different sites, offering a key mechanism that needs to be integrated into the modeling of biogeochemical nutrients cycling in karst ecosystems. [ABSTRACT FROM AUTHOR]

Excess N deposition has aroused concerns about its negative impacts on forest ecosystems. A two-year study was conducted to assess the responses of stomatal conductance (Gc) and carbon assimilation (Anet) of dominant tree species (Liquidambar formosana, Quercus acutissima and Quercus variabilis) to increased N deposition at a canopy and understory N additions experimental platform in a temperate deciduous broadleaved forest. Five treatments included N addition of 25 and 50 kg ha−1 y−1 onto either the canopy (C25 and C50) or the understory (U25 and U50), and a control treatment (CK, without N addition). Our results showed that neither canopy nor understory N addition had an impact on carboxylation capacity (Vcmax), the light saturated rate of electron transport (Jmax) and leaf-level net assimilation (AnL) of the studied tree species. Higher concentrations of N addition (U50 and C50 treatments) exerted negative impacts on Gc and Anet of L. formosana and Quercus acutissima under lower precipitation conditions, while lower concentrations of N addition (U25 and C25 treatments) had minimal impacts on overall ecophysiological function. The U50 treatment increased tree water use efficiency (WUE) of L. formosana in the second experimental year. Canopy and understory N addition generated differential effects on forest vegetation. The traditional approach with understory addition could not fully reflect the effects of increased N deposition on the canopy-associated assimilation processes. [ABSTRACT FROM AUTHOR]

Anthropogenic activities and climate change are exacerbating the occurrence of extreme rainfall that normally brings large amounts of nutrient-rich freshwater from the land to the sea, resulting in acute salinity decrease and nutrient increase. To evaluate the effects of such changes in salinity and nutrients, we tracked the changes in photosynthetic efficiency and growth of phytoplankton assemblages from the northern South China Sea at 5 salinity levels and at an intermediate salinity level with 3 or 4 nitrogen concentrations. The results showed that the reduction of salinity reduced the maximum photochemical quantum yield (F V /F M) of photosystem II of phytoplankton within a short-term cultivation (i.e. 24-72 h), followed by a stimulatory effect. The reducing effect of reduced salinity lasted longer in the nearshore area than in the offshore area, so the stimulatory effect occurred later in the former area. Nitrogen enrichment mitigated the negative effect of reduced salinity in short-term cultivation and showed a positive effect on F V /F M in long-term cultivation. Moreover, both reduced salinity and enriched nitrogen stimulated phytoplankton growth after an acclimation period. Our results suggest that the reduced salinity stresses phytoplankton in the short term, which is mitigated by nitrogen enrichment, but benefits them in the long term. This sheds light on how phytoplankton thrive and even flourish in coastal or estuarine environments where salinity and nutrients typically covary strongly after extreme rainfall. • Reduced salinity suppresses phytoplankton in the short term, but benefits it in the long term. • Reducing effect of reduced salinity lasts longer in offshore than nearshore areas. • Both reduced salinity and enriched nitrogen stimulated phytoplankton photosynthesis and growth in the long term. [ABSTRACT FROM AUTHOR]

Growing of Pyropia haitanensis, a commercially farmed macroalga, usually increases their densities greatly during cultivation in natural habitats. To explore how the increased algal densities affect their photosynthetic responses to rising CO2, we compared the growth, cell components and photosynthesis of the thalli of P. haitanensis under a matrix of pCO2 levels (ambient CO2, 400 ppm; elevated CO2, 1,000 ppm) and biomass densities [low, 1.0 g fresh weight (FW) L−1; medium, 2.0 g FW L−1; high, 4.0 g FW L−1]. Under ambient CO2, the relative growth rate (RGR) was 5.87% d−1, 2.32% d−1 and 1.51% d−1 in low, medium and high densities, and elevated CO2 reduced the RGR by 27%, 25% and 12% respectively. Maximal photochemical quantum yield of photosystem II (FV/FM) was higher in low than in high densities, so were the light‐utilized efficiency (α), saturation irradiance (EK) and maximum relative electron transfer rate (rETRmax). Elevated CO2 enhanced the FV/FM in low density but not in higher densities, as well as the α, EK and rETRmax. In addition, elevated CO2 reduced the content of chlorophyll a and enhanced that of carotenoids, but unaffected phycoerythrin, phycocyanin and soluble proteins. Our results indicate that the increased algal densities reduced both the growth and the photosynthesis of P. haitanensis and alleviated the elevated CO2‐induced negative impact on growth and positive impact on photosynthesis. Moreover, the elevated CO2‐induced reduction on growth and promotion on photosynthesis indicates that rising CO2 may enhance the loss of photosynthetic products of P. haitanensis through releasing organic matters. [ABSTRACT FROM AUTHOR]

Plant–soil feedbacks (PSFs) are plant-mediated changes to soil properties that ultimately influence plant performance, and can, thus, determine plant diversity, succession, and invasion. We hypothesized that PSFs influence invasion processes and that PSF mechanisms are largely driven by changes in soil properties produced by specific plant species. To test these hypotheses, we studied the effects of different soils collected from under common plant species on the growth of the invasive plant Phytolacca americana. We found that PSFs may interfere with invasion resistance because P. americana seedlings showed reduced growth (lower biomass) in soils collected from underneath some native species compared with soils collected from underneath P. americana and two non-native plants. We then selected eight co-occurring native and non-native plant species, and examined PSF dynamics and mechanisms in a pairwise conditioned soil greenhouse experiment. Plant species-specific conditioning effects regarding soil nutrients and enzyme activities were observed. Phytolacca americana had a high ability to use soil N, which may be related to its high invasion ability. Soil P was significantly lower in Quercus acutissima-conditioned soil, indicating that low P availability in Q. acutissima forests may enhance resistance to plant invasion. However, surprisingly, some native plants did not produce PSF effects that decreased the relative performance of invasive plants, nor did the invasive plants produce PSF effects that increased their own performance. We speculate that these PSF findings from greenhouse experiments cannot be extrapolated to field conditions because the litter and allelochemicals of some plants may be important for invasion resistance. [ABSTRACT FROM AUTHOR]

To investigate the effects of atmospheric nitrogen (N) deposition on water use characteristics and leaf traits of trees, we performed canopy (C50) and understory (U50) N additions as NH4NO3 of 50 kg N ha–1 year–1 in a deciduous broadleaf forest of central China. We measured xylem sap flux, crown area : sapwood area ratio (C a : A s), specific leaf area (SLA), mass-based leaf nitrogen content (Nmass) and leaf carbon isotope ratio (δ13C) of Liquidambar formosana Hance, Quercus acutissima Carruth. and Quercus variabilis Blume. Functional traits under different N addition treatments and their responses among tree species were compared and the relationship between xylem sap flux and leaf functional traits under N additions were explored. Results showed that under U50 sap-flux density of xylem significantly decreased for three tree species. But the effect of C50 on sap flux was species-specific. The decrease of sap-flux density with N additions might be caused by the increased C a/ A s. δ13C remained constant among different N addition treatments. The responses of SLA and Nmass to N additions were species- and N addition approaches-specific. The correlation of xylem sap flux with leaf traits was not found. Our findings indicate that the effects of canopy N addition on xylem sap flux and leaf functional traits were species-specific and it is necessary to employ canopy N addition for exploring the real responses of forest ecosystems to climate changes in the future researches. To predict the function of forest ecosystems in the future it is necessary to explore the responses of functional traits to environmental changes. The variations in water use and leaf traits with addition of nitrogen differed among tree species, except water use efficiency, which remained constant. Our findings indicate that the experimental approach for simulating atmospheric nitrogen deposition needed to be modified, and that increased nitrogen availability could affect the species composition of forests. [ABSTRACT FROM AUTHOR]

Abstract Increasing atmospheric nitrogen (N) deposition could profoundly impact structure and functioning of forest ecosystems. Therefore, we conducted a two-year (2014–2015) experiment to assess the responses of tree sap flux density (J s) and intrinsic water use efficiency (WUE i) of dominant tree species (Liquidambar formosana , Quercus acutissima and Quercus variabilis) to increased N deposition at a manipulative experiment with canopy and understory N addition in a deciduous broadleaved forest. Five treatments were administered including N addition of 25 kg ha−1 year−1 and 50 kg ha−1 year−1 onto canopy (C25 and C50) and understory (U25 and U50), and control treatment (CK, without N addition). Our results showed neither canopy nor understory N addition had an impact on leaf N content and C:N ratio (P > 0.05). Due to the distinct influencing ways, canopy and understory N addition generated different impacts on J s and WUE i of the dominant tree species. Canopy N addition increased WUE i of Q. variabilis , whereas understory addition treatment had a minimal impact on WUE i. Both N additions did not exert impacts on WUE i of L. formosana and Q. acutissima. Canopy N addition exerted negative impacts on J s and its sensitivity to micrometeorological factors of Q. acutissima and Q. variabilis in 2014, while understory addition showed no effect. Neither canopy nor understory N addition had an influence on J s of L. formosana in 2014. Probably owing to the increased soil acidification as the experiment proceeded, J s of L. formosana and Q. variabilis was decreased by understory N addition while canopy addition had a minimal effect in 2015. Thus, the traditional understory addition approach could not fully reflect the effects of increased N deposition on the canopy-associated transpiration process indicated by the different responses of J s and WUE i to canopy and understory N addition, and exaggerated its influences induced by the variation of soil chemical properties. Graphical abstract Unlabelled Image Highlights • Research was conducted at a novel platform with canopy and understory N addition. • N addition decreased J s and its sensitivity to PAR and VPD during some periods. • Canopy leaf N content was unaffected by external N addition. • Canopy N addition increased WUE i of Quercus variabilis. • Understory N addition could not fully reflect effects of increased N deposition. [ABSTRACT FROM AUTHOR]

Precipitation changes such as more frequent drought and altered precipitation seasonality may impose substantial impacts on the structure and functioning of forest ecosystems. A better understanding of tree responses to precipitation changes can provide fundamental information for the conservation and management of forests under future climate regimes. We conducted a 2-year seasonal rainfall redistribution experiment to assess the responses of tree transpiration and growth to manipulated precipitation changes in a subtropical evergreen broad-leaved forest. Three precipitation treatments were administered including a drier dry season and wetter wet season treatment (DD), an extended dry season and wetter wet season treatment (ED), and an ambient control treatment, with the total amount of annual rainfall being kept the same among the three treatments. Our results showed that the DD and ED treatments reduced daily transpiration of Schima superba by 8-16 and 13-25%, respectively. The ED treatment also reduced the DBH increment of larger S. superba individuals. In contrast, neither treatment showed obvious effects on the transpiration and DBH increment of another dominant species Michelia macclurei. However, the transpiration of both species showed clear inter-annual differences between the 2 years with contrasting annual rainfall (2094 vs 1582 mm). S. superba had a lower transpiration-to-precipitation ratio (T/P) compared to M. macclurei and showed decreased sensitivities to total solar radiation and vapor pressure deficit under the DD and ED treatments. These results indicate the deep-rooted S. superba may be suppressed with a lower ability to obtain water and assimilate carbon compared to the shallow-rooted M. macclurei under the precipitation seasonality changes, which could potentially cause shifts in species dominance within the forest community. [ABSTRACT FROM AUTHOR]

To assess the water use of a clumped bamboo species, Bambusa chungii , we modified original 20 mm long thermal dissipation probes (TDPs) by shortening each prototypical probe to 5 mm in length. Before applying the modified TDPs in the field, we calibrated the measured sap flow ( J S ) against gravimetric measurements ( J g ) with a cut experiment with B. chungii culm and corrected J S derived transpiration with actual water loss from a pot experiment under outdoor conditions. The validated TDP underestimated J S by 27.5% compared with the actual water loss from the pot. The optimal sample sizes of J S and culm area ( A C ) were evaluated to be 17 and 8 with random sampling, respectively. Meanwhile, the former was shown to be a lower value based on the stratified method ( n = 15), mirroring the age effect on the J S variances. As a result, the annual stand transpiration for three clumps during the field experiment (January 2014–December 2014) was 397.0 mm with an error of 7.77% (considering the individual variance of J S and A C ) when all of the sample culms ( n = 45) were pooled together. This transpiration value was lower than that of a native broadleaf species Schima superba stand (461 mm) and higher than a widely planted Eucalyptus urophylla stand (327.4 mm) that grew nearby when the same microclimatic conditions were assumed. However, the unlimited transpiration with increased VPD indicated the potentially increased pressure on the regional water balance. [ABSTRACT FROM AUTHOR]

Research results on the effects of environmental factors on tree water use, growth, and water use efficiency vary latitudinally and geographically and the conclusions remain controversial. In this study, we investigated the tree transpiration (E t), basal area increment (BAI), and water use efficiency (WUE) of a typical plantation tree species, Schima superba , in South China, aiming to identify the dominant environmental factors in regulating and affecting the tree water use and growth. Datasets including the continuously measured sap flow and meteorological parameters, as well as the periodically measured diameter at breast height and height of observed sample trees, were collected during the period from 2008 to 2021. The redundancy analysis results indicated the significant effects of air temperature (T) and humidity (RH) on tree E t , BAI, and WUE. According to Pearson correlations among the environmental factors, we divided them into "Heat group" and "Water group", and conducted the variation partitioning analysis. Results highlighted that it was the heat factors including air temperature and solar radiation rather than the water factors that explained the larger variations of E t , BAI, and WUE. The abundant total precipitation in South China and the ability to take advantage of deep soil moisture of S. Superba weakened the role of water but emphasized the effect of heat. Considering the current growth and the water use of S. superba , and the obvious climate changes in recent decades in South China, it is concluded that this species can maintain its growth under the current climate conditions. Overall, our study demonstrates a more important role of heat factors compared to water factors in regulating tree water use, growth and WUE in subtropical S. superba plantations, which could offer a promising implication for the management of subtropical plantations under future climate trajectories. • Both BAI and WUE of S. superba presented an increase trend during the past 14 years. • Heat factors played a critical role in regulating tree transpiration, BAI and WUE. • Water factors showed weak explanations for tree transpiration, BAI and WUE. [ABSTRACT FROM AUTHOR]

Canopy stomatal ozone (O 3 ) flux ( F st,O3 ) in a plantation of Schima superba , an ecologically and economically important evergreen pioneer tree species in subtropical China, was quantified based on sap flow measurements during a 2-year period. Mean F st,O3 and accumulated F st,O3 ( AF st 0) were significantly higher in wet seasons from April to September (4.62 nmol m − 2 s − 1 and 35.37 mmol m − 2 , respectively) than in dry seasons from October to March (3.90 nmol m − 2 s − 1 and 24.15 mmol m − 1 , respectively), yet comparable between the 2 years of the experiment, being 4.23 nmol m − 2 s − 1 and 58.23 mmol m − 2 in April 2013–March 2014 and 4.29 nmol m − 2 s − 1 and 60.80 mmol m − 2 in April 2014–March 2015, respectively. At the diurnal scale, F st,O3 generally peaked in the early to middle afternoon hours (13:00–15:00), while the maximum stomatal conductance ( G st,O3 ) typically occurred in the middle to late morning hours (09:00–11:00). Monthly integrated AF st 0 reached the maximum in July, although accumulated O 3 exposure ( SUM 0) was highest in October. Seasonally or yearly, the accumulated O 3 doses, either exposure-based or flux-based, notably exceeded the currently adopted critical thresholds for the protection of forest trees. These results, on the one hand, demonstrated the decoupling between the stomatal uptake of O 3 and its environmental exposure level; on the other hand, indicated the potential O 3 risk for S. superba in the experimental site. Therefore, the present study endorses the use of sap flow measurements as a feasible tool for estimating F st,O3 , and the transition from the exposure-based toward flux-based metrics for assessing O 3 risk for forest trees. Further studies are urgently needed to relate stomatal O 3 uptake doses with tree growth reductions for an improved understanding of O 3 effects on trees under natural conditions. [ABSTRACT FROM AUTHOR]

Canopy stomatal uptake of NO X (NO, NO 2 ), SO 2 and O 3 by three mature urban plantations (of Schima superba, Eucalyptus citriodora and Acacia auriculaeformis ) were studied using the sap flow-based approach under free atmospheric conditions. The annual mean concentration for NO, NO 2 , SO 2 and O 3 were 18.2, 58.1, 12.8 and 42.4 μg m −3 , respectively. The atmospheric concentration exhibited a spring or winter maximum for NO, NO 2 and SO 2 , whereas the concentration maximum for O 3 occurred in the autumn. Despite the daytime mean canopy stomatal conductance ( G C ) being positively related with the photosynthetically active radiation ( PAR ) and negatively with the vapour pressure deficit ( VPD ), the maximal daytime mean G C did not appear when the PAR was at its highest level or the VPD was at its lowest level because a positive correlation was noted between the daytime mean PAR and VPD ( P < 0.001) under field conditions. The G C value was regulated by the cooperation of the PAR and VPD . When analysing the respective effect of the PAR or VPD on G C separately, a positive logarithmical correlation was noted between the daytime mean G C and PAR as the following equation: G c = a × lnPAR − b ( P < 0.01), and the daytime mean G C was negatively logarithmically correlated with the VPD : G c = G sref − m × lnVPD ( P < 0.001). The daytime mean G C declined with decreases in the soil water content ( SWC ) under similar meteorological condition. Differences in the seasonal pattern of the canopy stomatal conductance and atmospheric concentrations led to a differentiated peak flux. The flux for NO, NO 2 and SO 2 exhibited a spring maximum, whereas the flux maximum for O 3 appeared in the autumn or summer. The annual cumulative stomatal flux for NO, NO 2 , O 3 and SO 2 was 100.19 ± 3.76, 510.68 ± 24.78, 748.59 ± 52.81 and 151.98 ± 9.33 mg m −2 a −1 , respectively. When we focus on the foliar uptake of trace gases, the effect of these gases on the vegetation in turn should be considered, particularly for regions with serious air pollution problems. These trace gases had not yet reached injury levels, except for NO 2 . Flux-based measurements were better suited for evaluating the risk of O 3 damage to vegetation than the exposure-based method. [ABSTRACT FROM AUTHOR]

7 b SEM for the relationships among climatic factors, plant family composition, and leaf nutrient stoichiometry. Numbers above the arrows indicate the path coefficients (the pathway was significant at 0.05 level and all the path coefficients were standardized), R SP 2 sp values are the proportion of variance explained for each variable. [Extracted from the article]

Quantifying the sensitivity of trees to environmental variables such as vapor pressure deficit ( D ) is important for understanding the hydrological responses to land use changes and the role of underlying physiological mechanisms. Sap flux ( J s ), water transport, and sensitivity of canopy stomatal conductance ( G s ) to D ( m ) were determined during the early dry season in 2012 and 2013 for young timber trees (5 years), secondary forest trees (∼25 years), and mature forest trees (∼50 years) at three sites of lower subtropical China. The J s was found to be negatively correlated with tree biometric parameters, and whole tree water transport for a given tree size decreased with age or size, which was partially attributed to the lower sapwood quantity for a given diameter. The m and reference G s at 1 kPa ( G sref ) of the seven tree species decreased from young timber to mature trees, although not significantly. The D , which is the extrapolated value when stomata closure ( e b/m ), significantly varied among species, which decreased from isohydric Eucalyptus grandis × urophylla to more anisohydric Acacia auriculiformis and Eucalyptus citriodora . J s and maximum sap flux ( J s,max ) decreased with wood density, suggesting that water flux was regulated by biophysical constraints. Wood density was a good predictor of G sref ( r 2 = 0.664, P = 0.026), indicating that water flux to D is an intrinsic adaptive characteristic. To the best of our knowledge, this is the first study linking wood density and G sref . The responses of water flux to D varied among species, size or age, and hydraulic architecture, which highlights that modeling water budget to land cover transition based on the same hydraulic parameter from one land use scenario can potentially cause extensive errors in model prediction. Our empirical research could be used for the evaluation of the consequences of land use changes on the hydrological process of forest ecosystems. [ABSTRACT FROM AUTHOR]

In order to study the effects of latitudinal change in physical and chemical environments on phytoplankton cells, we investigated the early summer phytoplankton biomass, species composition and size-fractioned productivity in surface water from the Java Sea to the South China Sea (from 6°S to 20°N) from 18 May to 27 May 2010. Chlorophyll a (Chl a) concentration decreased latitudinally from 0.18 (∼6°S) to 0.05 µg l–1 (∼10°N). The dominant species, the cyanobacteria Trichodesmium erythraeum, dinoflagellates (e.g. Gyrodinium dominans, Amphidinium carterae and Gonyaulax spp.) and diatoms (e.g. Thalassionema nitzschioides, Rhizosolenia spp. and Chaetoceros spp.) changed to only the dinoflagellate species. Also, the Chl a biomass increased to 0.14 µg l–1 towards the end of the survey (∼20°N) with the dinoflagellates as the most abundant group. Productivity of phytoplankton assemblages coincided with Chl a concentration, and decreased accordingly from 9.24 ± 0.71 to 2.87 ± 0.41 µg C l–1 day–1, then increased to 5.45±1.1 µg C l–1 day–1. Chl a concentration and productivity were significantly correlated (P<0.05) with microplankton cell abundance, as well as nutrient concentrations, which appeared to exert a strong influence over latitudinal variation in primary production. [ABSTRACT FROM AUTHOR]

Quantifying the water use effects of tree plantations on regional hydrological processes is vitally important for evaluating the reforestation strategies related to a sustainable use of water resources. We conducted a comprehensive study to investigate the precipitation partitioning and hydrological effect of three different plantations (Schima wallichii , Acacia mangium , and Cunninghamia lanceolata) by monitoring sap flow and using a water balance equation during a two-year period (from January 2017 to December 2018) in hilly lands of South China. Owing to the abundant precipitation and radiation, both monthly stand-scale transpiration and evapotranspiration of the tree plantations were higher in the wet season than in the dry season. Strong stand-scale transpiration (T stand) and evapotranspiration (ET) were observed in the broadleaved S. wallichii and A. mangium with a large proportion (more than 90%) of ET in precipitation (P). Whereas the coniferous C. lanceolata plantation possessed lower T stand and ET but higher surface runoff, indicating a water surplus for the water yield. Following the uneven distribution pattern of precipitation, clear seasonal variation was observed for the ratio of ET/ P that exceeded 1 during majority of the dry season. The observed vigorous transpiration and the higher ET/ P values of the broadleaved S. wallichii and A. mangium plantations than those of the coniferous C. lanceolata suggests that broadleaved plantations are more likely to pose a potential threat to the catchment water yield and water balance in this region. However, the C. lanceolata, which limited the water exchange between the atmosphere and plants, is also considered to prevent its growth. Our findings quantified the hydrological effects of different plantations and will help to address the increasing water resource concerns related to the rapid expansion of plantations in hilly lands of South China. • Broadleaved plantations presented a higher stand scale transpiration (E T) than the coniferous plantation. • More than 90% of precipitation was used for evaportranspiration (ET) in broadleaved plantations. • The coniferous plantation possessed lower E T and ET values but higher surface runoff. • High E T and ET/ P values of broadleaved plantations possibly suggested a decrease in catchment water yield. [ABSTRACT FROM AUTHOR]

• Stem corticular photosynthesis is beneficial to hydraulic maintenance of Eucalyptus trees. • The change of stem photosynthesis could trigger adaptive adjustment of leaf photosynthesis. • Stem corticular photosynthesis increases drought resistance of Eucalyptus trees. Different from leaf photosynthesis that depends on stomatal uptake of CO 2 , stem green tissue mainly uses internal CO 2 for re-assimilation. Research attention has moved to its specific effect on xylem hydraulic function, however, the effect of stem corticular photosynthesis on whole-plant water transport and leaf photosynthesis during drought stress of varying intensities remains unexplored. To fill this knowledge gap, we designed stem shading treatments on Eucalyptus urophylla trees in the field and its seedlings in the greenhouse with soil water-controlled experiment. Sap flow density (J s), whole-plant hydraulic conductance (K plant), stem tissue fluorescence parameters and stem non-structural carbohydrates (NSC) were measured. Stem shading treatments caused the decrease of K plant and J s of E. urophylla trees, more importantly, the increase of K plant and J s with the recovery of corticular photosynthesis after shading removal was observed in the field experiment. The main effect of shading treatment on stem NSC concentration of E. urophylla seedlings is a decrease, which was not influenced by soil water conditions. Moreover, the shading effects on leaf gas exchange vary with drought intensity, under severe drought stress, stem shading caused a significant decline of stomatal conductance (g s,) and leaf maximum net photosynthesis (A max) for E. urophylla seedlings. These findings suggested that stem corticular photosynthesis plays a compensatory role in maintaining whole-plant hydraulic conductance integrity and water transport of E. urophylla. The remarkable negative impact of stem shading on leaf gas exchange implying a possible interconnection between leaf and stem photosynthesis, which highlights the potential significance of stem photosynthesis in drought stress resistance under changing climate regimes. [ABSTRACT FROM AUTHOR]